Annular lens antenna



March 12, 1957 N. M. RUST ETAL 2,785,397

ANNULAR LENS ANTENNA Original Filed Sept. 9, 1947 5 Sheets-Sheet lINVENTORS A/OEL M. Ausrmva Jay E Imus/1r Fr rakA/z) March 12, 1957 N. M.RUST ETAL 2,785,397

ANNuLAR LENS ANTENNA Original Filed Sept; 9, 1947 I5 Sheets-Sheet 2INVENTORS A va M 057' we BY JOHN E was irramvzr March 12, 1957 N RUSTETAL 2,785,397

ANNULAR LENS ANTENNA Original Filed Sept. 9, 1947 3 Shets-Sheet 3 .65 Hl l VENTORS A/ozz M $057 #w JOHN F Kiwis/9r fi-rram fr United StatesPatent ANN ULAR LENS ANTENNA Noel Meyer Rust and John Forrest Ramsay,Chelmsford, England, assignors, by mesne assignments, to RadioCorporation of America, New York, N. 1., a corporation of DelawareApplication January 2, 1951, Serial No. 214,450, now Patent No.2,764,757, dated September 25, 1956, which is a division of applicationSerial No. 772,960, September 9, 1947, now Patent No. 2,650,985, datedseptember 1, 1953. Divided and this application April 1, 1955, SerialNo. 502,062

14 Claims. (Cl. 343-753) This invention relates to radio horns, that isto say horn-like devices for directing very high frequency radio energy.Radio horns have a considerable field of application e. g. tocommunication systems, navigation aiding systems (especially foraircraft use) and radar systems.

This application is a division of co-pending U. S. application SerialNo. 214,450, filed January 2, 1951, by the same joint applicants as thepresent application, which in turn is a division of original U. S.application Serial No. 772,960, filed September 9, 1947, by the samejoint applicants of the present application. The said originalapplication issued on September 1, 1953 as Patent No. 2,650,985. Theco-pending application issued on September 25, 1956, as Patent No.2,764,757.

One of the difficulties encountered in the use of horns whether fed bywave guides or other means is that the lengths of the paths from thesmall end or virtual apex of the born to different points in the planeof its aperture are different with the result that the field is notuniform in phase over the said plane and, in general, uniformity ofphase of field over the aperture is necessary to eflicient radiation. Inthe case of a horn of wide aperture in relation to the wave length, andof length comparable to the aperture, this defect becomes serious, beingvery detrimental to the directivity of the horn, and imposes seriousconstructional limitations since if a good standard of directivity is tobe maintained the horn must be made of great length which results eitherin excessive bulk or expensive and complicated folding. The presentinvention seeks to reduce or avoid this defect and the limitationsresulting therefrom.

The invention is based upon the fact that the phase of field in a spacebounded on at least two sides by conductive walls placed parallel to theelectric field and not less than half a wave length apart progresses ata velocity greater than the velocity in free space, this increase. invelocity resulting from the interaction of waves reflected from theboundary walls. This field velocity or phase velocity may be controlledby controlling the spacing of the boundary walls, this spacing being, ofcourse, always not less than a half wave length.

The present invention is based upon the above men tioned physicalphenomenon and consists in its main feature in utilising the saidphenomenon to compensate for the effect of different path lengthsbetween apex and aperture of a horn so as to ensure that despitedifferent path lengths there is a predetermined phase distribution whichis usually required to be uniformity of phaseover the said aperture. Thesimplest and most common case is that in which the aperture lies in ageometrical, i. e. a flat plane, but the invention is not limited tothis case and may be employed in cases in which the aperture lies on acurved surface e. g. a cylindrical surface. Again the aperture need notactually be across the mouth ice of a horn proper; as will be seen laterit may be across the mouth of an attachment to a horn, the attachmentbeing then regardable as part of a horn structure consisting of the hornproper and the attachment.

According to the main feature of this invention a radio horn structurecomprises means for differently modifying the velocity of propagationover different paths from apex to aperture so as to compensate orcorrect to a desired degree for the effects of the different lengths ofsaid paths on phase distribution across said aperture.

The invention is illustrated in and further explained in connection withthe accompanying drawings.

There are various methods by which the invention may be carried intoeffect and these methods may be used either singly or in conjunction.

One method is to provide horn partition plates of predetermined shape,extent and disposition which in effect divide up the horn into waveguide sections so dimensioned as to produce increase of velocity (ascompared to the velocity in free space) so as to compensate fordifferent path lengths in the horn and give uniformity of phase acrossthe aperture.

Another method is to provide a horn with an attachmerit whose innerspace is subdivided by suitably shaped and disposed plates into what arein effect wave guides which produce velocity changes such thatuniformity of phase is obtained at the aperture of the attachment.

A third method consists in constricting the horn by giving it what maybe termed delayed flaring up or ad vanced flaring down, that is to say,flaring up or down so as to produce required velocity changes tocompensate for different path lengths.

The invention will be described in greater detail by reference to thefollowing description taken in connec tion with the accompanying drawingwherein similar reference letters refer to similar elements and inwhich:

Figures 1 and 2 are crosssectional and end views respectively of anembodiment of the invention including a wave-guide horn flared in onedimension only;

Figure 3 is across-sectional view of an embodiment of the inventionwherein the horn is flared in two dimensions;

Figure 4 is a partially cut-away, perspective view of the embodiment ofFigure 3;

Figure 5 is a partially cut-away, perspective view of an embodiment ofthe invention including a horn extension with a bi-concaveelectromagnetic lens positioned there in;

Figures 6-9 are cross-sectional Views of various electromagnetic lens.arrangements according to the invention;

Figure 10 is a partially cut-away, perspective view of an alternativeembodiment of the invention similar to the one shown in Figure 4;

Figure 11 is a partially cut-away, perspective view of an embodiment ofthe invention employing stepped-back lens plates;

Figures 12 and 12a are perspective and plan views, respectively, of anelectromagnetic lens mounted in the extension of a folded horn;

Figures 13 and 14 are respective cross-sectional and end views of anelectromagnetic lens positioned in a skew horn;

Figures 15 and 16 are respective cross-sectional and end views of anelectromagnetic lens positioned in a skew horn: the lens and horn are ofdifferent types than the ones shown in Figures 13 and 14; and

Figure 17 is a perspective view of a bi-cone antenna arrangementincluding an electromagnetic lens according to the invention.

Referring to Figures 1 and 2 which show in diagrammatic section and endview respectively one embodiment ,of the invention as applied to a hornflared out in one plane only for use with waves with polarisationperpendicular to the plane of flaring, the horn is divided into what arein effect a series of wave guide sections GS by means of plates P atright-angles to the parallel walls of the horn the plates being radialas viewed in a direction perpendicular to said parallel walls (re asviewed in Figure 1) so that the plates all point from the mouth of thehorn towards the apex. The plates nearest the flared walls are longestand diminish in length towards the centre of the horn so that thevelocity increase in the outermost wave guide sections is greater thanthat in the more inward sections whereby the greater lengths of theouter paths from apex to aperture are compensated. Typical practicaldimensions in terms of the wave length (2) are indicated in Figure l.

The principle embodied in the construction just described may beextended as shown in Figures 3 and 4 to a horn which is flared in bothplanes. Figure 3 is a diagrammatic axial section and Figure 4 aperspective view.

As will be seen the sub-dividing plates are not only of varied lengthbut their inner edges are curved (see Figure 4) whereas in the case ofFigures 1 and 2 for a horn flared in one plane only the ends of thesub-dividing plates may be simply straight.

In another class of embodiment, instead of providing path lengthcorrecting velocity increasing plates in the flared part of the horn, astraight rectangular horn extension may be provided and suitably shapedand disposed sub-dividing plates mounted across the extension so thatalthough there will not be uniformity of phase where the energy entersthe extension there will be the desired uniformity across What is nowthe effective aperture of the whole horn structure (comprising hornproper and extension) i. e. where the energy leaves the extension.Plates subdividing such an extension into wave guide sections may besimple rectangular plates of different sizes or they may be plates withinner curved edges. Figure 5 is an embodiment of this nature, the hornproper being indicated at H and the extension at X, the plates curved onboth edges, being shown at P. Figure 11 illustrates an alternativeembodiment, this one employing stepped-back double concaveelectromagnetic lens plates. The particular arrangement in any case willdepend upon design requirements and the plates will be horizontally orvertically disposed in dependence upon the plane of polarisation.

For all embodiments in accordance with this invention the partitionplates may be of uniform spacing with their lengths varied or they maybe of uniform length with their spacing varied or both spacing andlength may be varied to provide the required compensation. These threepossibilities are indicated in Figures 6 to 8, Figure 6 showing constantspacing and varied length, Figure 7 showing varied spacing and constantlength and Figure 8 showing both length and spacing varied. Again thespacing of the plates may, if desired, be varied over the individuallengths of the wave guide sections formed thereby. Where both length andspacing are varied the design may be and preferably is such that eachwave guide section is an integral number of half wave lengths long, i.e. an integral number of half wave lengths in the wave guide. Thisdesign expendient has the advantage of facilitating matching theimpedance of the born to the impedance of a feeding wave guide.

The methods of carrying out the invention which consist in providingpartition walls in a horn or in an extension to the horn may be employedin combination. For example, a horn structure may comprise as shown inFigure 9 a horn proper H and a parallel sided box like extension X withpartition plates P shaped and dimensioned to produce the requiredcompensation for different path lengths arranged in the extension memberand also extending into the horn proper. In the case shown the partitionplates P are angularly bent where they pass from the horn proper H intothe extension X,

parts of the plates lying parallel to the extension axis and parts lyingparallel to the flared sides of the horn proper as shown. The plates Pmay be bent over as indicated and by suitable adjusting the angles ofbending of the individual plates a degree of control of the amplitudesof the energies entering the individual wave guide sections GS and adegree of control of the amplitude distribution across the horn therebyobtained. This is indicated in Fig. 9 by showing alternative angles ofbending for two of the plates in broken lines.

This arrangement of partition plates parallel to the walls of a horn orextension, through probably the simplest to design is not essential forit will be apparent from a consideration of first principles that otherarrangements can be utilised since the wave guide sections into which ahorn proper and/or an extension is or are divided in carrying out thisinvention need not be of uniform cross section nor such as to provide aconstant velocity of propagation along their lengths. The requirement ofthe invention is that the modification of velocity of propagationproduced by the subdivision into what are in effect wave guide sectionsshall be such as to compensate, as regards phase distribution across aflat or curved surface constituting the aperture for different lengthsof path between the feeder wave guide or line and the aperture and sofar as fundamental considerations are concerned it is of secondaryimportance whether the velocity modification if eflected uniformly ornot.

Where it is desired to produce a horn of wide aperture in the E plane(electric plane) but narrow aperture in the H plane (magnetic plane) theopposite to delayed flaring may be used, i. e. the narrowing down fromfeeder wave guide dimension to the required narrow aperture dimensionmay be carried out earlier for the outer paths than for the inner andcentral paths, the design being again such as to produce a substantiallyequi-phase aperture. In order to avoid defects due to the ray pathsbeing bent by refraction it is desirable, and in some cases may be foundessential, to provide suitably disposed metal plates normal to thedirection of the electric field at the entrance to the phase correctingpart of the horn and extending along this part in such a way as to guidethe Wave elements. These plates should not be confused with those whichdivide a horn with wave guide sections, for the latter are parallel tothe electric field and therefore at right angles to the former. Againsuch metal plates which extend normal to the electric field and to theextension of the velocity modifying plates and which may be termedbaffles may be provided in other constructions in accordance with thisinvention, e. g. in a horn extension, the baflles, in conjunction withthe velocity modifying plates then resulting in a honeycomb like orcellular structure. An arrangement of this type is shown at BP in Figure10. It is understood that any other of the arrangements may likewise beprovided with baffle plates.

The expedients of velocity modification by delayed flaring up or flaringdown; by constriction; and by partition plates sub-dividing the hornplates into wave guide sections may be adopted in any desiredcombination each of the expedients adopted contributing its quota to thetotal velocity modification introduced. Further the methods of theinvention are not limited to their application to straight horns forobviously they may be employed also for folded horns. Figures 12 and 12ashow a folded horn with an extension X housing plates P. They are alsovery advantageous when applied to the construction of what may be termedskew horns or part horns." This is a very important class of embodimentpractically. In one embodiment of this class illustrated in the mutuallyperpendicular views of Figures 13 and 14 a skew horn or part horn H is,in effect, a normally shaped horn which is cutaway along a planeparallel to the axis for example along a plane passing through theaxis-and mounted on a fiat surface (e. g. the ground G) with the planeof cutting on that surface. Thus where the cutting plane passes throughthe axis the result would be a halfhorn resting on the flat surface.

By means of partition plates P and/ or flaring provided in accordancewith this invention the phase distribution across the mouth of the halfhorn may be made such as to give a directional beam parallel to the axisalthough the horn is not geometrically symmetrical with respect to theaxis. The plates P may be bent over and, as in Fig. 9 a degree ofcontrol of the amplitude distribution across the horn obtained bysuitably adjusting the angles of bending (indicated in broken line forone plate). Figures 15 and 16' show another construction of this typefor the case where the electric fieldis at right-angles to that forFigures l3 and 14. In Figures 13 and 15 the direction of the electricfield is indicated conventionally at E. The great practical advantage ofthis type of construction is that the energy feeding apparatus at thesmall end of the horn may be brought at or near ground or buildinglevelan advantage leading to great constructional convenience andeconomy.

The principles of the invention may be extended to socalled bi-coneswhich produce circular polar diagrams, in all horizontal planes and arelatively sharp beam in all vertical planes. For example in the case ofa bi-cone exciting vertically polarised waves phase correction may beeffected by vertical partition plates of suitable varying profilearranged radially round the periphery of the bi-cone structure. In thecase of a bi-cone excited by bent dipoles or by loops to produce anall-round horizontally polarised field, phase correction may be effectedin accordance with this feature of the invention by providing aplurality of parallel peripheral ring plates round the bi-cone structureand of different radial lengths, those nearest the centre being shorterthan the outer ones. In the case of bi-cones with very large cylindricalapertures it is very convenient to omit the outer parts of the bi-cone.In such a case a suitable construction of partition plates may beprovided at a little distance from the actual bi-cone orifice. One formof bi-cone structure in accordance with the invention is illustrated, inFigure 17 in which the bi-cone BC with energy radiating slots at S isprovided with ring plates P.

In all cases in accordance with this invention in which the pathdifferences to be corrected for exceed a wave length, that is to say inwhich the lengths of the paths for which correction is to be appliedexceed the shortest path by one or more wave-lengths, it is necessaryonly to correct for such path diiferences in excess of a wave length oran integral number of wave lengths will clearly not introduce any phasechange. In other words partition plates or other devices provided incarrying out this invention may be of stepped construction being steppedback at each point or points corresponding to a path difference of anintegral number of wave-lengths as shown in Fig. 11. Further althoughthe partition plates and other conducting surfaces have beenspecifically described as plates or surfaces of solid material it willbe obvious to those skilled in the art that they may be perforated forlightness or to reduce windage or made of wires or gauze (as may bedesired) for the same reasons and the term plates is intended to coverall such constructions.

Although the invention has been described with reference to thetransmission of radio energy it will be apparent to those skilled in theart that the constructions described herein may also be used forreception if desired since a radio horn is in essence a reversibledevice.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be performed, we declarethat what we claim 1. A radio antenna system comprising waveguidetransmission means including a pair of conductive conical surfacesarranged to define a waveguide having a centrally located throat portionadapted to be coupled to a radio frequency transducer and an apertureopen to free space, and a plurality ofv annular plates arranged at saidaperture to compensate for the effects of different path lengths withinsaid passage on the phase distribution of the energy at said apex andsaid aperture.

2. An antenna comprising a central radiator or receptor for radio wavesat an operating frequency and having a radiation pattern substantiallynon-directional about a predetermined axis, a stack of substantiallyparallel metallic plates surrounding and spaced from said radiator orreceptor and spaced in the axial direction each from the next adjacentplate by more than a half free-space wavelengthat the operatingfrequency, each said plate being disc-like with inner and outer edgeseach substantially a complete circle coaxial with said axis, the axialspacing between plates and the dimension of each plate radially fromsaid inner to said outer edge being selected to cause a relative shiftin phase between radio waves at the operating frequency polarized withthe electric vector normal to said axis and thus parallel to said platesand propagated-radially between one pair of adjacent plates and thosesimilarly polarized and similarly propagated between an adjacent pair ofplates, said shift in phase at plates centrally located along said axisbeing progressively less than and in retardation of those more remotefrom said central plates, whereby the said antenna is nondirectional ina plane normal to said axis, and the directivity in a plane through saidaxis is increased over that of said central radiator or receptor.

3. The antenna claimed in claim 2, said outer edges all having the sameradii.

4. The antenna claimed in claim 2, said plates all having the same inneredge radii and the same outer edge radii and the spacing between onepair of adjacent plates differing from that between the next adjacentpair.

5. An antenna comprising, in combination, a source providing anomnidirectional radiation pattern in a given plane; and means forincreasing the directivity of said pattern in planes perpendicular tosaid given plane including a plurality of parallel, spaced, annularconductive plates lying in planes parallel to said given plane, eachformed with a central aperture, the edges of said plates defining thecentral apertures therein lying in a generally concave, continuous,cylindrical, contour surface, said source being arranged centrally inthe volume included within said contour surface.

6. An antenna comprising, in combination, a source providing anomnidirectional radiation pattern in a given plane; and means forincreasing the directivi'ty of said pattern in planes perpendicular tosaid given plane including a plurality of spaced, parallel, aligned,annular conductive plates lying in planes parallel to said given plane,each of the same diameter, and each formed with a central aperture, theedges of said plates defining the central apertures therein lying in agenerally concave, continuous, cylindrical, contour surface, and theouter edges of said plates lying in a plane, continuous, cylindrical,contour surface, said plurality of plates being concentrically arrangedabout said source.

7. An antenna as set forth in claim 5, and further including a firs-tconductive surface member defining an at least approximately conicalsurface extending from said source to one of the end conductive platesof said plurality of plates, and a second conductive surface memberdefining an at least approximately conical surface extending from saidsource to the other end conductive plates of said plurality of plates,said conductive surface members being arranged with said surfaces inaxial alignment and forming between them an electromagnetic waveguidingpassage.

8. In combination, a pair of juxtaposed conductive surface members eachdefining an at least approximately conical surface, said members beingspaced apart with said surfaces in axial alignment and forming anelectromagnetic waveguiding passage between them, said passage having acontinuous circular aperture; and a lens arrangement positioned in saidaperture of said waveguiding pass age, said arrangement including aplurality of spaced apart, parallel annular conductive plates concentricwith the common axis of said surface members, each said plate beingformed with a central aperture, the edges of said plates defining'saidcentral apertures lying in a generally concave, continuous, cylindrical,contour surface.

9, in the combination set forth in claim 8, the outer edges of saidplates defining a plane, cylindrical, contour surface.

10. An antenna comprising waveguide transmission means formed as a pairof continuous, annular, conductive surfaces of generally biconicalcross-section concentric with an axis, said means including a centrallylocated throat portion and an annular aperture open to free space; andplurality of annular partition plates arranged concentric with said axisat said aperture for differentially modifying the velocity ofpropagation of the wave energy translated through said aperture tocompensate for the effects of diiferent path lengths traversed bycomponents of said wave energy on the phase distribution of said energyat said apex and said aperture.

ll. in combination, antenna means having an omnidirectional antennapattern in a given plane; and means for increasing the directivity ofsaid pattern in planes perpendicular to said given plane including aplurality of parallel, spaced, annular conductive plates lying in planesparallel to said given plane, each formed with a central aperture, theedges of said plates defining the central apertures therein lying in acontour surface, said antenna means being arranged in the volumeincluded within said contour surface.

12. In combination, antenna means having an omnidirectional antennapattern in a given plane; and means for increasing the directivity ofsaid pattern in planes perpendicular to said given plane including aplurality of parallel, spaced, annular conductive plates lying in planesparallel to said given plane, each formed with a central aperture, theedges of said plates defining the central apertures therein lying in acontour surface, said antenna means being arranged centrally in thevolume included within said surface.

13. in combination, antenna means having an omnidirectional antennapattern in a given plane; and means for increasing the directivity ofsaid pattern in planes perpendicular to said given plane including aplurality of parallel, spaced, annular conductive plates lying in planesparallel to said given plane, each formed with a central aperture, theedges of said plates defining the central apertures therein lying in afirst contour surface, the outer edges of said plates lying in a planecylindrical contour surface, and said antenna means being arrangedcentrally in the volume included Within said first contour surface.

14. in combination, antenna means having an omnidirectional antennapattern in a given plane; and means for increasing the directivity ofsaid pattern in planes perpen dicular to said given plane including aplurality of parallel, spaced, annular conductive plates lying in planesparallel to said given plane, each formed With a central aperture, theedges of said plates defining the central aperture lying in a generallyconcave, cylindrical contour surface, and the outer edges of said plateslying in a plane cylindrical contour surface, said antenna means beingarranged centrally in the volume included Within said concave contoursurface.

References Cited in the file of this patent UNITED STATES PATENTS2,471,021 Bradley May 24, 1949

